Piezoelectric devices such as quartz crystal oscillators have been playing an important role in the field of communication because of their high characteristic stability. The advance of communication technology is now creating demands for smaller, high-performance, inexpensive piezoelectric or magnetic devices.
One conventional way of processing a crystal oscillator is described by reference to FIG. 21. In the first place, a quartz crystal is cut at a predefined cut angle. The temperature property of quartz crystal depends upon the cut angle; however, a quartz crystal is usually AT-cut into quartz crystal plates in order to make use of thickness shear mode vibrations. Such a quartz crystal plate is cut into desired dimensions and is polished for the adjustment of thickness. Then, the quartz crystal plate is subjected to an etch treatment to remove a layer suffering damage from such polishing. Electrodes are formed on both sides of the quartz crystal plate, thereafter the process of packaging is carried out.
The processing technique of FIG. 21, however, suffers from some problems. For example, when attempting to thin a quartz crystal plate so as to use a piezoelectric device at a high frequency, the technique of FIG. 21 has difficulties in polishing quartz crystal plates if they are very small. In other words, it is impossible to hold and polish a tiny quartz crystal plate having a thickness of, say, ten odd micrometers without breaking it. A solution to such a problem may be found by changing the order of processing steps. That is, a quartz crystal plate is first polished to an adequate thickness. This is followed by an etching process. Then, the quartz crystal plate is cut. With this solution, the mass productivity may be accomplished. If a finished quartz crystal plate is extremely thin, however, this causes breakage at cutting time.
Japanese Patent Application, published under Pub. No. 4-367111, shows a technique in which a reinforcement member is provided to prevent a quartz crystal plate from breaking. More specifically, this technique shows a metal supporter with springiness that supports a piezoelectric oscillator. In this technique, the oscillation of the piezoelectric oscillator may be checked when it is being held by the metal supporter and thus special attention should be given to the packaging method.
Japanese Patent Application, published under Pub. No. 5-121985, shows another technique. In this technique, a great number of crystal oscillators are fixed to a substrate using an adhesive agent; however, such a packaging technique becomes very difficult to carry out because the size of crystal oscillators decreases with increasing the degree of high-frequency. Generally, the resonant frequency of piezoelectric oscillators is required to be adjusted roughly prior to packaging. This, however, may not applicable to small oscillators because it is not easy to individually handle them during the preparation and adjustment process, thereby creating an obstacle to mass production. Furthermore, the piezoelectric oscillators are held with the aid of an adhesive agent, resulting in poor resistance to heat and vibration.
U.S. Pat. No. 5,036,241, entitled "Piezoelectric Laminate and Method of Manufacture", shows a technique. In this technique, a plate-like piezoelectric body is laminated to a dielectric body using an adhesive agent. The value of the dielectric's resistivity is controlled by means of temperature and light. A voltage is applied to the dielectric body, whereby electric polarization occurs. However, when attempting to process devices based on resonant in the thicknesswise direction of the piezoelectric body, the thickness of an adhesive layer as a result of using the adhesive agent must be controlled precisely because the accuracy of resonant frequency is determined by the accuracy of the piezoelectric body's thickness direction. If a piezoelectric is formed by an AT-cut quartz crystal plate and the center frequency is 100 MHz, the thickness of the piezoelectric will thin down to about 17 .mu.m. In such a case, accuracy of 1 .mu.m or less is required with consideration of the mass productivity and time required for adjustment. Therefore, this technique in which errors in adhesive layer thickness directly contribute to the frequency accuracy may not be practical because it is extremely difficult to control the thickness of the adhesive layer with a high precision.
Other techniques are known in the art. For instance, a paper entitled "Film Bulk Acoustic Wave Resonator Technology" (1990 Ultrasonic Symposium Proceeding, page 529) and U.S. Pat. No. 4,719,383 entitled "Piezoelectric Shear Wave Resonator and Method of Making Same" each show a crystal filter. A crystal filter is formed as follows. A buffer layer of SiO.sub.2 is formed on a substrate of silicon or gallium arsenide. Then, a thin film of aluminum nitride or zinc oxide and an electrode are formed to make up a resonator or crystal filter. Piezoelectrics of aluminum nitride or zinc oxide used in this technique can be formed by a thin film technology known in the art as sputtering. Thin films thus formed are polycrystalline, so that, in order to obtain good piezoelectric effects, it is necessary to make the C axis of each crystal grain orient along the normal of the thin film. Such orientation depends on the film process parameters, on the film forming apparatus, on the deposition thickness, and on the substrate material type. Neither quartz, lithium niobate, nor lithium tantalate exhibits good piezoelectricity if they are in the form of a polycrystalline structure. Because of its good stability and thermal property, quartz crystal finds applications in crystal oscillators and filters; however, only .alpha. quartz that is a single crystal with a 3-fold rotation axis crystal structure exhibits the piezoelectric effect.
As described above, conventional piezoelectric device processing techniques have difficulties in improving dimensions accuracy that influences high-frequency properties as well as in accomplishing mass production while at the same time maintaining good piezoelectricity. Similar difficulties apply in techniques of processing electronic components such as magnetic devices.